The present invention is related to a solder disposed configuration for a heat resistant structure, more particularly, related to a configuration of a solder disposed on a substrate so as to prevent the heat resistant structure deformation from the thermal stress.
Traditionally, a heat resistant structure is used as a catalytic converter under high temperature condition for purifying the exhaust gas in an engine. The heat resistant structure disposed between the exhaust outlet and the tailpipe of an engine (e.g. vehicle engine) is composed of a honeycomb structure fitted and fixed into a hollow cylindrical shell, wherein the honeycomb structure is formed by the solders on a substrate to weld and join a flat and a corrugated sheet together so as to be used for noxious emission and purifying the exhaust gas.
A substrate of the typical heat resistant structure is usually made of with a substantially uniform thickness of the flat and the corrugated sheets. After rolling up or superimposing the sheets, the substrate is formed in a roll-shape by brazing or in a wound multilayered block by brazing multilayer.
The honeycomb structure is coated with the noble metal catalyst (such as platinum Pt, palladium Pd, and rhodium Rh) for purifying the exhaust gas. As to the noxious emissions, carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides NOx) may change to carbon dioxide (CO2), water (H2O), and nitrogen (N2) by the catalytic action. In the meanwhile, the exothermic reaction may increase the temperature. Because the speed of exhausted gas flowing through the honeycomb structure along the central axis is the fastest and along the outer periphery is the lowest, the thermal stress is generated by the difference between the high temperature of central axis and the low temperature of outer periphery. There are two mainly stresses, normal stress and shear stress, acting perpendicular and parallel to the cut surface of the substrate respectively. In general, the total substantially length of the corrugated sheet is 2-3 times of the flat sheet in a honeycomb structure, thus, the thermal expansion length of the corrugated sheet is 2-3 times of the flat sheet. The main reason of the honeycomb structure deformation is due to the shear stress paralleling to the cut surface of the substrate generated by the thermal expansion.
However, refer to the FIG. 1, the typical locations of the solder 132, 133 are on the plane surface U of the substrate 111 alongside both two edges R and L, similarly, the solder 131 and 134 are disposed on the plane surface D alongside both two edges R and L with any arbitrarily width respectively. The FIG. 2 shows the enlarged view of the principle part of a honeycomb structure 101, which is after rolling up the substrate 111 (shown in FIG. 1). Obviously, from an end view, the solders 131 and 132 will be located between the flat sheet 121 and corrugated sheet 122 after welding, and as a result, when the corrugated sheet 122 withstands the thermal expansion stress, it may cause deformation by the solders 131 and 312 fixing on the substrate 111. Particularly, there is no flexible space for the substrate 111 since the solders 131 and 132 are fixing on and between the flat and corrugated sheet 121 and 122. After high thermal welding, the solders 131 and 132 may be agglomerated into spot-form (as shown in FIGS. 2 and 3) by its surface tension. Furthermore, see the FIG. 2, the corrugated sheet 122 may be pushed toward in the direction X by thermal expansion, and the flat sheet 121 may hold it back due to the smaller measurement of thermal expansion. Consequently, the thermal stress is generated in the opposite direction X and Y for the honeycomb structure 101. Refer to the FIG. 4, the stress is increasing from the center to the outer of the honeycomb structure 101 for the conventional heat resistant structure 100 due to the thermal difference causing by the different speed of emission flowing, hence, see the FIG. 3, the point C of the flat and corrugated sheets 121 and 122 near the hollow cylindrical steel 102 may be cracked by the thermal stress.
In the U.S. Pat. No. 5,302,355 show an exhaust purifying device and method of producing the same. However, it only shows the structure of the honeycomb structure without indicating the disposition of the solder. Therefore, the present invention provides a solder disposed configuration for a heat resistant structure to have more flexible space for solder fixing between the corrugated sheet and flat sheet withstanding the thermal expansion stress. And furthermore, the present invention may be used in variety of the honeycomb structures for solving the problem of providing flexible space.
The present invention provides a solder disposed configuration for a heat resistant structure for forming a catalytic converter for purifying the exhaust gas in an engine. The heat resistant structure is composed of a honeycomb structure fitted and fixed into a hollow cylindrical shell. The honeycomb structure comprises at least a substrate having a flat sheet and a corrugated sheet. A first and a second strip of solder are disposed alongside a first and a second edge paralleling to each other on a first and a second plane surface of the substrate respectively, wherein the second plane surface is the reverse side of the first plane surface of the substrate, and the first and second edge are opposite to each other on the first and the second plane surface respectively for forming the honeycomb structure. Rolling up the substrate to form the honeycomb structure (e.g. spirally wound-form) by the solder disposed on the substrate to weld and join the flat and corrugated sheets together. Thereafter, heat them with high temperature and under vacuum condition to weld the solders for joining and fixing each other. Furthermore, the catalyst is coated on the surface of the heat resistant structure to form a catalytic converter for purifying the exhaust gas in an engine.
Accordingly, the solder disposed configuration for a heat resistant structure provided by the present invention may make the substrate having more flexible space in the two sides thereof. Therefore, the substrate has two flexible spaces for expanding and/or contracting under the high thermal stress so as to solve the conventional problem of honeycomb structure deformation causing by the lack of a flexible space.